The biosynthesis of proparathyroid hormone and its conversion to parathyroid hormone in mammalian parathyroid glands is under investigation. Emphasis is placed on the chemical structure of the prohormone, other peptides which may be related to the parathyroid hormone in a potential precursor role, the enzymes responsible for the conversion of the prohormone to parathyroid hormone, the packaging and secretion of parathyroid hormone and the control of these processes by calcium and other ions. In vitro studies are also planned on tumor tissue from patients suffering hypercalcemia related to malignancy to determine if this type of tissue synthesizes and secretes parathyroid hormone or a parathyroid hormone-like peptide. BIBLIOGRAPHIC REFERENCES: Huang, W.Y., Chu, L,L.H., Hamilton, J.W., McGregor, D.H., and Cohn, D.V. The NH2-Terminal Amino Acid Sequence of Human Proparathyroid Hormone by Radioisotope Microanalysis. Arch. Biochem. Biophys. 166:67, 1975. MacGregor, R.R., Hamilton, J.W., and Cohn, D.V. The By-Pass of Tissue Hormone During the Secretion of Newly-Synthesized Parathyroid Hormone. Endocrinology 97:178, 1975.